Laminating Mu Metal Core

Yes, that is normal industrial practice. I suppose you could try slow-setting super glue and a press to squeeze out excess goop. Find a way to measure the insulation thickness for both cases, and then the inter-lamination resistivity.

Si steel laminations are usually ordered with a coating such as C5:

For high permeability they need to be hydrogen annealed after punching.

Vacuum impregnation. The equipment may also apply a positive pressure after the vacuum has been released.

Sometimes they are welded (at one end only, obviously)

That might not be appropriate with mu metal.

--sp

You have to be super careful handling mu-metal, because if you bang it or bend it, its permeability drops like a rock until it's carefully re-annealed.

So I wouldn't use any sort of insulation that won't take the annealing temperature.

Cheers

Phil Hobbs

I have a reel of ebay metglas strip, very thin and flexible.

Filled epoxy, glass beads or sand or something, makes an insulating spacer. Cataphote?

or paper

NT

Probably wouldn't take 1100 C even in a hydrogen atmosphere. ;)

Cheers

Phil Hobbs

Double-sticky kapton tape?

The Kapton might be a bit over-kill, but I do have some double-sided newspaper splicing tape that is thin and has a plastic base.

Could be a fiddly and time consuming job though.

It's having to insulate each lamination that is tricky and prevents the use of lacquer.

Robert Miller

I don't run my transformers that hot :)

NT

Kapton is fabulous stuff. Its dielectric strength is amazing, 7000 volts/mil or something insane like that. Its emissivity is almost 1.0 at thermal wavelengths, so you can stick a bit on metal or something and image it.

It's affordable on ebay. Pretty amber color, too.

Soft steel (silicon iron, goes by many names) would be easier: that's what commercial laminations are made of. If it HAS to be mu-metal, you need to cut/form it, then anneal (for best performance). Hydrogen anneal is recommended, but that isn't nice to most coatings. As long as the spacing between uninsulated spots is larger than the thickness of the strips, it's good enough: just a bit of paint (the pigment grains are the key element) should suffice.

The mu metal used in D.T. transformers is around 30 layers per cm and uses a 1% thick Silicate coating that is quite durable, clamped for minimum gap.

I do like kapton tape, we use it to stick heater wire onto things... (glass and aluminum cylinders) Years in the field and I have yet to hear a complaint.

George H.

(knock on wood... not that I'm superstitious :^) GH

Google tells me it could mean "distribution transformer", but they are huge.

AFAIK Mu-metal core trannies are all small signal types.

.... Phil

Yes, I see there is a lot on eBay, but only single sided. How would you use it between multiple flat laminations to hold them together?

Robert Miller

OK. I found a few sellers that have double sided. Perfect. Thanks.

Robert Miller

Why mu metal and not regular transformer steel?

Oops. Just looked it up. Never mind.